1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for recording a radiation image on a stimulable phosphor, exposing the stimulable phosphor to stimulating rays which cause the stimulable phosphor to emit light in proportion to the stored radiation energy, detecting the emitted light to read out the radiation image, and converting the emitted light into an electric signal. This invention particularly relates to a radiation image recording and read-out apparatus which as a whole is small in size.
2. Description of Prior Art
When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a recording material provided with a layer of the stimulable phosphor is first exposed to radiation which has passed through an object such as the human body in order to store a radiation image of the object thereon, and is then two-dimensionally scanned by stimulating rays such as a laser beam which cause the recording material to emit light in proportion to the stored radiation energy. The light emitted by the recording material upon stimulation thereof is photoelectrically detected and converted into an electric image signal by a photodetector, and by using the image signal the radiation image of the object can be reproduced as a visible image on a recording medium such as photographic film, a display device such as a cathode ray tube (CRT), or the like.
The radiation image recording and reproducing system using a recording material provided with a stimulable phosphor is advantageous over conventional radiography using a silver halide photographic material in that the image can be accurately recorded even when the stimulable phosphor is exposed to a very wide range (latitude) of radiation energy intensities. More specifically, since the amount of light emitted upon stimulation after the radiation energy is stored on the stimulable phosphor varies over a wide range and is in proportion to the amount of said stored energy, it is possible to obtain an image having a desirable density regardless of the amount of radiation to which the recording material provided with the stimulable phosphor is exposed, by reading out the emitted light with an appropriate read-out gain and converting it into an electric signal in order to reproduce a visible image on a recording medium or a display device.
In the aforesaid radiation image recording and reproducing system, the recording material provided with the stimulable phosphor is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For reasons of economy, therefore, it is desirable that the recording material provided with the stimulable phosphor be reusable.
Accordingly, the applicant has proposed, for example in U.S. Pat. No. 4,543,479, a radiation image recording and read-out apparatus which enables the stimulable phosphor to be efficiently circulated and reused.
The proposed radiation image recording and read-out apparatus comprises, in a single apparatus:
(a) a supporting material,
(b) at least one recording material attached to said supporting material and comprised of a stimulable phosphor layer capable of storing a radiation image,
(c) an image recording section for exposing said recording material to radiation which has passed through an object in order to store a radiation image of the object on said recording material,
(d) an image read-out section provided with a stimulating ray source for emitting stimulating rays for scanning said recording material carrying said radiation image stored thereon, and a photoelectric read-out means for obtaining an electric image signal by reading out light emitted by said recording material scanned and stimulated with the stimulating rays,
(e) a means for circulating said recording material attached to said supporting material with respect to said image read-out section for enabling reuse of said recording material, and
(f) an erasing section for eliminating radiation energy remaining on said recording material prior to recording a next image on said recording material after the preceding radiation image has been read out therefrom at said image read-out section,
whereby the recording material is efficiently circulated and reused.
In the proposed radiation image recording and read-out apparatus, it is very advantageous for a material comprising an endless supporting belt with a plurality of stimulable phosphor layers overlaid on the endless supporting belt to be used as the recording material. In this case, the recording material can be applied around rollers or the like and conveyed and circulated sequentially through the image recording section, the image read-out section and the erasing section. An example of such a configuration is shown in FIG. 26.
With reference to FIG. 26, three stimulable phosphor sheets 602 are attached to an endless conveyor 601. The conveyor 601 is provided around rollers 603 and 604, and moved in the direction indicated by the arrow through rotation of the rollers 603 and 604. Around the conveyor 601, an image recording section 610, an image read-out section 620 and an erasing section 630 are disposed sequentially in the direction in which the conveyor 601 travels.
The image recording section 610 is provided with a radiation source 611 which may be an X-ray source or the like, and stores a radiation image of an object 612 on the stimulable phosphor sheet 602 which faces the radiation source 611 with the object 612 interposed. The stimulable phosphor sheet 602 carrying the radiation image thus stored thereon is then sent to the image read-out section 620. The image read-out section 620 is provided with a stimulating ray source 622 for emitting stimulating rays 621A such as the rays of a laser beam, a light deflector 622 constituted of a galvanometer mirror or the like for deflecting the stimulating rays 621A emitted by the stimulating ray source 621 across the width of the conveyor 601, and a photodetector 623 for reading out light 625 emitted by the stimulable phosphor sheet 602 upon stimulation thereof by the stimulating rays 621A. The photodetector 623 may be constituted of a head-on type photomultiplier, a photoelectric amplification channel plate or the like. The light 625 emitted by the stimulable phosphor sheet 602 upon stimulation thereof is guided by a light guide member 624 and then photoelectrically detected by photodetector 623. When the stimulable phosphor sheet 602 on which the image has been recorded has been sent to the image read-out section 620, the stimulable phosphor sheet 602 or the scanning system for the stimulating rays 621A and the system for detecting the light 625 emitted by the stimulable phosphor sheet 602 are moved normal to the direction in which the stimulating rays 621A scan, so that the overall surface of the stimulable phosphor sheet 602 is exposed to the stimulating rays 621A and image read-out is carried out over the overall surface of the stimulable phosphor sheet 602. After the image is read out from the stimulable phosphor sheet 602, the stimulable phosphor sheet 602 is sent to the erasing section 630, which is provided with an erasing light source 631. The erasing light source 631 irradiates light having a wavelength within the stimulation wavelength range of the stimulable phosphor sheet 602 onto the stimulable phosphor sheet 602 to cause it to release any radiation energy remaining thereon. The erasing light source 631 may be constituted of, e.g., a tungsten-filament lamp, a halogen lamp, an infrared lamp, or a laser light source as disclosed in U.S. Pat. No. 4,400,619. The stimulable phosphor sheet 602 erased at the erasing section 630 is again sent to the image recording section 610. In the course of moving to the erasing section 630, the stimulable phosphor sheet 602 is cleaned by a cleaning roller 605, which removes dust from the sheet surface.
However, with the radiation image recording and read-out apparatus shown in FIG. 26, wherein the image recording section and the image read-out section are disposed to face the same surface (the upper surface) of the conveyor, the length of the overall apparatus in the horizontal direction is several times the length of a stimulable phosphor sheet used to store a single radiation image, and therefore the apparatus as a whole is very large. As is well known, the aforesaid radiation image recording and reproducing system is used to great advantage when making medical diagnoses. However, because the recording and reproducing apparatus comprising the recording and read-out apparatus is large, the apparatus can only be installed centrally in a comparatively large-scale hospital, and it is not always possible to install such an apparatus in each medical examination room in a comparatively small-scale hospital. Also, with the aforesaid recording and read-out apparatus the stimulating rays scan the conveyor as it moves between two rollers, and therefore the scanning position on the phosphor sheet is unstable, for example it swings as the conveyor is moved. Therefore, the accuracy of the scanning often deteriorates.